With the development of Ethernet, service providers pay more and more attention to the maintainability of devices. As Ethernet expands to MAN (metropolitan area network) and WAN (wide area network), various problems about the transport network need to be solved. Most of the problems about the transport network may be solved via Operation, Administration and Maintenance (OAM) functions. The Ethernet OAM mainly includes:
1. The automatic detection of a failure. The detection of a failure may be accomplished by connectivity check (CC). Specifically, during CC, a source node sends a CC frame, i.e. a CC message, to a destination node periodically, and the destination node periodically receives the CC message; and if the destination node does not receive the CC message from the source node after a period of time, it will give an alarm. The connectivity and continuity of a link are checked by checking CC messages, so that the object of end-to-end automatic detection of failures may be attained.
2. Positioning of a failure. The positioning of a failure may be accomplished via loop back (LB). Specifically, during LB, after a source node sends a loop back message to a destination node, it waits for a loop back response from the destination node; if no loop back response from the destination node is received in a specific time period, it will give an alarm. A failure point is positioned mainly by such a two-way connectivity check.
3. The isolation of a failure. During link tracing (LT), a source node sends an LT message manually, and after a MIP (maintenance intermediate point) receives the message, it returns a response to the source node, and forwards the message to downstream nodes at the same time until it reaches the destination node. As a result, the topological structure of the link may be discovered, so that a failure may be isolated according to the topological structure of the link.
The reliability of the network can be improved by the above-mentioned three functions of OAM, thus the maintainability of the network can be enhanced.
In the above three functions, all source nodes need to send unicast message to destination nodes according to the MAC address of each destination node. Wherein, the source node and the destination node both belong to an MP (maintenance point), which includes a MIP (maintenance intermediate point) and a MEP (maintenance end point); the source node can only be a MEP, while the destination point can be a MIP or a MEP.
If a source node does not know the MAC address of a destination node, it cannot send a unicast message to the destination node. However, the OAM proposals only puts forward that an identifier should be allocated to a MP, but not point out how each MP can obtain the MAC addresses of other Mps.